設計模式之（一）Factory模式

敏捷式軟體開發 (Agile Software Development)-原則、模式與實踐

依賴倒置原則（DIP）說的是任何類都應依賴於抽象類別，避免依賴於具體類。

Circle c = new Circle(r);

Circle是一個具體類，所以建立Circle的勢力都違反了DIP。很多具體類都是

非常易變的，依賴於他們會帶來問題。這就用到了Factory模式，factory模式

允許只依賴於抽象介面就能建立具體對象的執行個體。

下面是個具體的例子

//Client.java

package com.factory;
import static org.junit.Assert.*;
import org.junit.Test;
public class Client {
@Test
public void testFactory() {
ShapeFactory sf = new ShapeFactoryImpl();
Shape s = sf.make("Circle");
assertTrue(s instanceof Circle);
}
}

//ShapeFactory.java

package com.factory;
public interface ShapeFactory {
Shape make(String shapeName);
}

//Shape.java

package com.factory;
public abstract class Shape {
}

//Circle.java

package com.factory;
public class Circle extends Shape {
}

//ShapeFactoryImpl .java

package com.factory;
public class ShapeFactoryImpl implements ShapeFactory {
@Override
public Shape make(String shapeName) {
if(shapeName.equals("Circle")) {
return new Circle();
} else {
return null;
}
}
}